i9o6. SEE-THE CAUSE OF EARTHQUAKES. 277 



depends upon the explosive pozver of steam formed within or just 

 beneath the heated rocks of the earth's crust chiefly by the leakage 

 of the ocean beds. 



Some of the most complicated phenomena in nature depend 

 upon the simplest and most obvious of causes, but there are several 

 reasons why the true cause often proves very difficult to discover. 

 On the one hand our mental operations are not infrequently 

 thwarted by conflicting prejudices and contradictory theories, so 

 that attention is diverted from the real questions ; and, on the other, 

 our clearness of vision and power of intuition are blinded by the 

 very closeness and familiarity of the true cause, which is least sus- 

 pected. Success in interpreting nature depends upon a combination 

 of the proper elements of thought into one simple connected view 

 which deals not with details but with the general tendencies. In the 

 case of earthquakes and volcanoes this general view has been very 

 difficult to obtain ; and with the growth of elaborate scientific inves- 

 tigation and classification of earthquakes the difficulty has increased 

 rather than diminished. For attention has been given to the 

 attainment of high accuracy in the measurement of tremors by 

 seismographs and other apparatus, and investigators have been oc- 

 cupied with the registration and discussion of the details of phe- 

 nomena rather than with the general underlying causes. 



We shall hereafter examine the porosity of matter and the prob- 

 lem of the penetration of water into the rocks of the earth's crust, 

 both from the experimental and historical standpoints, but let us 

 first consider the probable state of the internal heat of the earth. 

 In Astron. Nach., No. 4053, the writer has shown that when we 

 consider the force of gravity alone, and suppose a body to be made 

 up of gas reduced to the state of single atoms, over one-half of the 

 primordial supply of heat is stored up within the condensing mass, 

 while still in the gaseous stage ; and in a later paper on the rigidity 

 of the heavenly bodies {A. N., 4104), it is shown that circulation 

 and radiation become retarded and greatly restricted with increasing 

 density, so that in the later stages of the development of a mass like 

 the earth, much more than one-half of the heat generated is retained 

 within the mass for raising the temperature. It is shown that all 

 the heat of our earth depending on gravitation would raise the 



